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Apache ZooKeeper: Reverse-DNS fallback enables hostname verification bypass in ZooKeeper ZKTrustManagerGHSA-7xrh-hqfc-g7qr

HIGHFix: apache/zookeeper@66c4efe

GHSA-7xrh-hqfc-g7qr is a high-severity (CVSS 7.4) CWE-295 vulnerability in org.apache.zookeeper:zookeeper. A fix is available for org.apache.zookeeper:zookeeper — see the affected versions and patch details below.

Also known asBIT-zookeeper-2026-24281CVE-2026-24281
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Oct 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-7xrh-hqfc-g7qr.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk+0.01%
Lower risk than most CVEs49th percentile — riskier than 49% of all scored CVEsHighest risk
0.00%0.38%0.76%1.15%0.0%0.6%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-7xrh-hqfc-g7qr by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected
☕org.apache.zookeeper:zookeeper☕org.apache.zookeeper:zookeeper

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

Hostname verification in Apache ZooKeeper ZKTrustManager falls back to reverse DNS (PTR) when IP SAN validation fails, allowing attackers who control or spoof PTR records to impersonate ZooKeeper servers or clients with a valid certificate for the PTR name. It's important to note that attacker must present a certificate which is trusted by ZKTrustManager which makes the attack vector harder to exploit. Users are recommended to upgrade to version 3.8.6 or 3.9.5, which fixes this issue by introducing a new configuration option to disable reverse DNS lookup in client and quorum protocols.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.apache.zookeeper:zookeeper≥ 3.8.0&&< 3.8.63.8.6org.apache.zookeeper:zookeeper:3.8.6
☕Mavenorg.apache.zookeeper:zookeeper≥ 3.9.0&&< 3.9.53.9.5org.apache.zookeeper:zookeeper:3.9.5

Affected Products

1 product · 2 configurations
Application
zookeeperapache
≥ 3.9.0 && < 3.9.5
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.zookeeper:zookeeper, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.apache.zookeeper:zookeeper to 3.8.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-7xrh-hqfc-g7qr is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant
Workaround published by Red Hat
To mitigate this issue, disable reverse DNS lookup in Apache ZooKeeper's client and quorum protocols. This can be achieved by configuring the `zookeeper.ssl.hostnameVerification.disableReverseDns` property to `true`. This configuration option is available in Apache ZooKeeper versions 3.8.6 and 3.9.5 and later. A restart of the ZooKeeper service will be required for the change to take effect.
Source: Red Hat security advisory for GHSA-7xrh-hqfc-g7qr (CC BY 4.0)
ProductFixed inAdvisory
Red Hat AMQ Broker 7.12.7zookeeperRHSA-2026:14276
Red Hat JBoss Enterprise Application Platform 6.0.7.GAorg.apache.zookeeper/zookeeper:3.8.4.redhat-00018RHSA-2026:70421
Streams for Apache Kafka 2.9.4zookeeperRHSA-2026:34608
Red Hat OpenShift AI 2.25rhoai/odh-modelmesh-rhel9:1776756834RHSA-2026:10184

Frequently Asked Questions

Hostname verification in Apache ZooKeeper ZKTrustManager falls back to reverse DNS (PTR) when IP SAN validation fails, allowing attackers who control or spoof PTR records to impersonate ZooKeeper servers or clients with a valid certificate for the PTR name. It's important to note that attacker must present a certificate which is trusted by ZKTrustManager which makes the attack vector harder to exploit. Users are recommended to upgrade to version 3.8.6 or 3.9.5, which fixes this issue by introducing a new configuration option to disable reverse DNS lookup in client and quorum protocols.
O3 Security · Impact-Aware SCA

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